An immunogenic 24 kDa calcium binding protein is found in Trypanosoma cruzi and is termed flagellar calcium binding protein (FCaBP). FcaBP is modified by the addition of myristate and palmitate to its amino terminus. These modifications mediate its localization to the flagellar plasma membrane. Calcium binding is also required for localization. Thus, FcaBP is similar to recoverin a calcium-myristoyl switch protein of the mammalian retina. FcaBP binds calcium through the third and fourth EF hand domains in distinction from recoverin which is modified only by myristate and binds calcium through the second and third EF hand domains. FcaBP is a novel calcium-acyl switch protein. We will extend our studies of FcaBP in a five-year research effort, the Specific Aims of which are: (i) determination of the mechanism for the flagellar membrane localization of FcaBP, (ii) identification of FCaBP partner proteins, (iii) elucidation of the calcium-myristoly/palmitoyl switch mechanism and (iv) characterization of Typanosoma brucei calcium acyl switch proteins.